Attention and cognitive load modulate motor resonance during action observation.

Observation of others' actions evokes a motor resonant (MR) response, in the parieto-frontal Action Observation Network (AON, comprising BA40, BA6, BA4). In order to investigate the effect of cognitive processes on the AON we manipulated attention and cognitive load during central and peripheral observation of hand grasping actions with three experiments. Motor Evoked Potentials (MEPs) were elicited in the opponent of the thumb (OP) and abductor of the little finger (ADM) by Transcranial Magnetic Stimulation (TMS) of the primary motor cortex. First, we investigated the role of selective attention by asking subjects to focus their attention on the thumb of the moving hand in central vision. A selective facilitation of OP MEPs was recorded, without the expected ADM MEPs modulation. Second, a "covert attention" paradigm was used to investigate the role of attention in peripheral vision. Surprisingly, MEP modulation was virtually abolished. In the third experiment we tested the hypothesis that the higher cognitive load introduced by the covert attention instruction had interfered with MR. We allowed subjects to view the action before its peripheral presentation with covert attention, thereby decreasing the cognitive effort necessary to decode the grasping action. The accuracy of motor resonant response was restored.